1. Field of the Invention
The present invention relates to a structure of a front end of a side-view type endoscope on the side surface of which a view window is provided.
2. Description of the Related Art
FIGS. 12 and 13 show a perspective view and a sectional side view of a front end portion of a known side-view type endoscope, respectively.
A front end body 1 provided at the front end of an insertion portion of an endoscope is made of corrosion resistant metal such as stainless steel and a view window 4, an illumination window 5, and a treatment tool insertion opening through which a treatment tool extends are provided on the side surface thereof.
A front end cap 30 which is made of an elastic material such as fluoro-rubber is in the form of a cylinder with a closed bottom and is provided with an opening 31 corresponding to the view window 4, the illumination window 5, and the opening 6.
The end cap 30 is detachably attached to the front end body 1. The end cap 30 is detached from the front end body 1 in FIG. 12 and is attached to the front end body 1 in FIG. 13.
When the front end body 1 is capped with the end cap 30, a peripheral projection 32 provided on the inner peripheral surface of the end cap 30 at the rear end thereof is fitted in a peripheral groove 7 formed on the outer peripheral surface of the rear end of the front end body 1.
The front end body 1 is provided on the front end surface thereof with a stepped portion 1a against which the end cap 3 abuts to prevent the end cap 30 from rotating relative to the front end body 1.
To detach the end cap 30 from the front end body 1, the portion of the insertion portion of the endoscope that is located adjacent to the rear end of the front end body 1 and the front end portion of the end cap 30 are held by the fingertips, respectively, as shown in FIG. 14. Then the end cap 30 is pulled forward and moved downward to disengage the same from the stepped portion 1a, as indicated by an arrow "A", so that the end cap 30 is partly detached from the front end body 1. In this state, the end cap 30 is pulled further forward, the end cap 30 is completely detached from the front end body 1, as shown in FIG. 15.
However, in the detachment operation, there is a stress concentration at the corner portions of the rear end of the opening 31. Consequently, there is a possibility that cracks 100 may occur in the rear corner portions of the opening 31 when the attachment and detachment of the end cap 1 to and from the front end body 1 are repeatedly performed. The same would be true when the front end of the insertion portion is moved while the front end of the end cap 30 is pressed hard against a mucous membrane in the body cavity of a patient.
If the cracks 100 are produced, the end cap 30 can be partly or completely detached from the front end body 1 within the body cavity of a patient during an examination using the endoscope. Consequently, the front end body 1 which is made of metal is exposed, so that the mucous membrane can be injured by the exposed front end body 1.